This invention relates to a process for improving the properties of polycarbonate compositions by addition of a property improving amount of a metal dodecylbenzenesulfonate. In particular, the invention relates to improving the processability by lowering the melt viscosity of polycarbonate compositions while also maintaining or improving impact strength.
Polycarbonates are resins in which groups of dihydric or polyhydric phenols are linked through carbonate groups. Generally, these resins can be formed from any dihydroxy compound in any carbonate diester, or by ester exchange. Polycarbonate resins are characterized by the --OCOO-- hetero chain unit. A common general purpose polycarbonate may be formed by reaction of bisphenol A with phosgene to produce: ##STR1##
There are many commercial sources of polycarbonate compositions including Dow Chemical Company, Mobay Chemical Corporation, Rohm & Haas Company, etc. Polycarbonates have many sought after properties such as high impact strength, good electrical properties, dimensional stability, rigidity, etc. Plus, polycarbonate compositions have been widely applied in such diverse applications as housewares, medical equipment, automotive applications, construction, plumbing, lighting components, furniture, business machines, food containers, etc. See, e.g., "Polycarbonate," Modern Plastics Encyclopedia 1981-1982, Vol. 58, No. 10A, 46 and 527-528 (McGraw Hill, Inc., 1981).
Although polycarbonate compositions have many desirable physical properties for which they are widely used; polycarbonates are difficult to process due to a high melt viscosity. Materials which have a high melt viscosity necessitate the use of higher processing temperatures and thereby increase energy costs of processing relative to the processing of similar materials having lower melt viscosity.
Therefore, plasticizers are usually incorporated into a material. Plasticizers increase a material's workability, flexibility, or distensibility. The addition of a plasticizer may lower the melt viscosity, the second order transition temperature or the elastic modulus of a plastic. Plasticizers may sometimes be utilized as processing aids to lower the processing temperature without altering the usefulness of the final product. See generally, "Plasticizers," Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 18, 3rd Ed., 111-177 (J. Wiley & Sons, Inc., 1982).
A typical polycarbonate such as that synthesized from bisphenol A, is characterized by a high hot-melt viscosity, which makes fabrication difficult. It is known that incorporation of about 0.2-5 weight percent of a suitable plasticizer, e.g., an aliphatic carbonate, can aid fabrication.
Polycarbonate compositions are compatible with a wide variety of plasticizers, including alkyl aryl hydrocarbons, adipates, benzoates, cyanamides, glycolates, phosphates, phthalates, pyromellitates, aryl sebacates, and sulfonamides. Most of these are compatible up to 100 phr (parts per hundred parts of resin) or higher. At high plasticizer concentrations and at elevated temperatures, the resin molecules are mobile enough to crystallize in the plasticizer exudes. Crystallinity can be avoided by quench-cooling. Little broadening of the elastomeric range is observed with most plasticizers. Generally the material behaves as a plasticized amorphous resin. Plasticizers with moderately high polarity usually provide the best results. It is also known that polycarbonate is unusually subject to antiplasticization by some plasticizers, e.g., BBP and Santicizer 8. See "Plasticizers," supra, at 160.
Disadvantageously, some desirable physical properties can be impaired by the use of these known processing aids in conjunction with polycarbonate compositions. In particular, addition of processing aids which lower melt viscosity can also detrimentally lessen the impact strength of the modified polycarbonate compositions.